OCEAN BASINS

Ocean Basins

• Continental margin
• Passive
• Active
• Deep sea floor
• Mid-ocean ridge

• Trench

Continental Margins

• Passive
• Continental shelf
• shallow, flat, very gently sloping continental area submerged by sea water
• composed of sediments overlying continental crust
• extension of the coastal plain
• Continental slope
• relatively steep (3° to 6°) area of continental margin
• transition between continental shelf and rise
• Continental rise
• sedimentary apron at base of continental slope
• overlies transition between continental and oceanic crust
• Active - continental margin bordering a trench
• narrow continental shelf
• continental slope but no continental rise - sediments dumped in trench

Continental Margins (cont.)

• Other features
• Submarine canyons
• cut by turbidity currents - very dilute slurries of sediment and water
• Abyssal fan
• fan-shaped sedimentary deposit on continental rise
• analogous to alluvial fan

Abyssal Fans

• Indus and Bengal Fans

Deep Sea Floor

• Abyssal hills
• rough volcanic topography
• ocean in sediment-starved ocean basins (Ex: Pacific Ocean)
• Abyssal plain
• flattest feature on Earth
• forms from sediment deposition that buries rough volcanic features
• terrigenous sediment - sediment derived from land
• pelagic sediment - sediment deposited far from land; derived from marine organisms (coccoliths, foraminifera)
• terrigenous sediments deposited by turbidity currents - turbidites

Deep Sea Floor (cont.)

• Mystery of the breaks in the Trans-Atlantic telegraph cable

Deep Sea Floor (cont.)

• Abyssal plain
• where sedimentation is very slow get manganese nodules
• potato sized nodules of Mn and Fe oxides
• grow very slowly (1 mm/m.y.)

Mid-Ocean Ridges

• Mid-Ocean Ridge
• Transform faults
• area between ridges where crust (and plates) show relative motion
• Fracture zones
• chasm formed as a result of faulting
• Rift valley
• central valley in mid-ocean ridge
• tension causes down-faulting of blocks

Origin of Ocean Basins

• Rifting (Fig. 11-17a)
• rifting beginning; not flooded
• little or no basalt
• Ex: African Rift Valley, Imperial Valley, CA
• Linear sea
• flooded with seawater but not true ocean
• Ex: Red Sea, Gulf of California
• Mature ocean basin
• true ocean; still widening
• Ex: Atlantic Ocean

• Declining ocean basin
• true ocean
• ringed by subduction zones; becoming smaller
• Ex: Pacific Ocean
• Terminal ocean basin
• no longer a true ocean; subducted
• Ex: Mediterranean Sea